Method of and means for treating gases



Aug.'3, 1954 s. c. cQLu-ms METHOD OF AND MEANS FOR TREATING GASES 2SheetsSheet '1 Original Filed Oct. 18 1949 [7206222021- fiamazei660225226.

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S. C. COLLINS Aug. 3, 1954 METHOD OF AND MEANS FOR TREATING GASESOriginal Filed Oct. 18 1949 2 Sheets-Sheet 2 b :IZIIII [220622202 1Samzze? 650222223.

Patented Aug. 3, 1954 METHOD OF MEANS FOR. TREATING GASES Samuel 0.Collins, Watertown, Mass, assignor to Joy Manufacturing Company,Pittsburgh, Pa, a corporation of Pennsylvania Original applicationOctober 18, 1949, Serial No. 122,077. Divided and this applicationOctober 1, 1953, Serial No. 383,436

11 Claims.

This invention relates to improvements in methods of and means fortreating gases.

It will herein be described particularly in its application to theproduction of substantially pure oxygen from air, but this is butillustrative, because the process and apparatus disclosed may be used,with appropriate adaptations, with various gases to be processed, toproduce various particularly desired products which are constituents ofthe gases to be treated. Under some circumstances the desired productmay be delivered at a relatively very high pressure and under others ata pressure of a few atmospheres.

It is very common, in the production of oxygen by a process involvingcooling and rectification of compressed air, to have it desirable tohave.

the oxygen available in gaseous form at a pressure substantially abovecolumn pressure but, on the other hand, much below cylinder pressure(cylinder pressure is on the order of 2000 p. s. i.). For example,oxygen may be desired at a pressure on the order of 50 p. s. i., thoughthis is but illustrative, and indeed the reference to oxygen is butillustrative also, because other gases which may be obtained by asimilar process may also be desired at pressuresabove column pressure.Re-

frigeration can be saved, taking the case of oxygen for purposes ofillustration, by taking gaseous rather than liquid oxygen from a pointin a column above the level of the liquid oxygen therein and boostingthe pressure from the few p. s. i. (perhaps 5) which exists at thatpoint in the column, to the desired delivery pressure :by the use of acompressor. This is, however, objectionable because of the additionalpower required and because of the size of the gaseous oxygen compressorwhich would be required. It is, I have found, much preferable to takeliquid oxygen from the column and to pump it at the desired pressure tothe oxygen supply line. This permits the use of much smaller pumpingequipment. It would, however, result in wasted refrigeration if someprovision were not made for using the heater vaporization of liquidoxygen in some manner. This heat or" vaporization, I have found, may beutilized by condensing an equivalent amount of air on its way to therectifier, as by bringingan appropriate-amount of air at an appropriatepressure and temperature into heat exchange relation with the leavingoxygen at a pressure substantially above condenser and be'condensed,when the temperature is reduced to, say, 112 K.'and the heat-removed toeffect the condensation is absorbed'by heat transfer within theevaporator-condenser byan outwardly flowing stream of initially liquidoxygen, and the oxygenmay bevaporized at 107 K. and '50- p. s. i, by theheat absorbed from the compressed air as the latter is liquefied. Suchan arrangement will involve a minimum loss of refrigeration andconcurrently avoid the need for a larger-size oxygen pump, and therewill be a conservation'of power because the work of. raising thepressure of liquid oxygen through a pressure range of 40 -p.'s. i.orsowill be much less than is required similarly toincrease the pressure ofan equal'masso'f gaseous oxygen. It will be evident that with ahighercompressed air supply pressure, liquid oxygen at 'a higher pressure maybe vaporized in theevaporator-condenser.

'It will also be evident that even if the delivery pressure of theoxygen (or other desired gas) should have to be substantially in excessof the pressure at which the liquid oxygen might "be vaporized in theevaporator-condenser, refrigeration could 'be saved and the size andpower requirements of the pump for gaseous oxygen which might be neededto bring the oxygen delivery change relation with leaving oxygen neednot the just such as to be completely liquefied by the refrigerationprovided by vaporizing the oxygen, butthat more than just that weight ofair can be put through the evaporator-condenser, and have completeliquefaction effected as later explained. Moreover, the air :usuallypassed through the evaporator-condenser may be diverted to the expansion"engine when, due to fortuitous circumstances, the expansion enginerequires more-air, and thus a more flexible systerm may be provided.

It is thus among the objects of the invention of this application toprovide asimple'compact, flexible apparatus'of the double-column typefor the efficient separation of gases, in which the requisiterefrigeration is provided "by a portion of the app'arat'us'in which thedesired en'dproductmay be produced with a purity of 99.5% or better,in'wh'ich, due toth'e eflective removal of impurities and the resultantavoidance of plugging of portions of the apparatus by the impurities,longer periods of operation may be possible, in which the accumulationof liquid for the placing of the unit in operation may be speeded up,and in which refrigeration may be conserved and the end product, in theillustrative embodiment oxygen, may be obtained with apparatus ofminimum size and power consumption at a pressure substantially abovecolumn pressure. A still further object of the invention is to providean improved method for the separation of gases, and more particularlyfor the separation of air, and the recovery in a desired nearly purestate of a constituent thereof. Other objects and advantages of theinvention will hereinafter appear.

In the accompanying drawings, in which apparatus by which the methodaspect of the invention may be practiced, and in which single and doublecolumn apparatus are shown for purposes of illustration:

Fig. 1 is a diagrammatic view of a single column apparatus; and

Fig. 2 is a similar view of a double column apparatus embodying theinvention.

Referring first to the system shown in Fig. l of the drawings, air at atemperature of approximately 300 K. and a pressure of 169 p. s. i. (allpressures are gauge unless otherwise indicated) may be delivered, asfrom a suitable air compressor (not shown), through a conduit H to avalve mechanism generally designated 52, and the efliuent (mainlynitrogen) leaving the apparatus may be discharged to the atmospherethrough a conduit 13. The valve mechanism i2 is of the mechanicallyactuated type, and is periodically moved by power, and with a snapaction, to reverse the connections of the conduits l l and 13 with apair of conduits l5 and 16 which lead from the casing of the valvemechanism i2. In the Samuel C. Collins application Serial No. 661,253,filed April 11, 1946, there is diagrammatically shown a reversing valvemechanism suitable for the performance of the functions of the valvemechanism 12; and an example of other mechanisms suitable for thispurpose forms the subject matter of Patent No. 2,638,923, granted May19, 1953 upon an application of Win W.

Paget, Serial No. 35,092, filed June 25, 1948. The

power for shifting the valve mechanism 12, to effect connection of theair supply conduit I i now with the conduit l5 and again with theconduit [6, and connection of the conduit 13 with the conduits l6 and [5while the conduit H is connected with the conduits l5 and It, may betaken from any suitabl source, but is desirably taken from the driveshaft of an expansion engine [8, through any suitable reducing gearingsuch as that which is diagrammatically illustrated in said Collinsapplication, Serial No. 661,253. Reverse-ls are adapted to be eifectedat relatively short intervals; and suitable intervals may be on theorder of three minutes.

Heat exchangers 2i and 22, desirably vertically disposed, and formed asseparate units, instead of as one longer unit, in order to keep heightwithin desirable limits, are arranged in series, and entering air passesthrough the heat exchangers 2i and 22 in the order mentioned, whileleaving nitrogen passes through these same heat exchangers in the order22, El. Heat exchanger 2! has three courses, indicated as coaxialcourses 21A, 25B, and MC, the first the innermost course and the lastthe outermost; and

exchanger 22 has similarly relatively arranged courses 22A, 22B and 22C,and, outside 220, a fourth course 22D. Through two of the courses inseries in the exchangers 2i and 22, to wit, courses 21B, 22B and courses21C, 22C, the entering air and the leaving nitrogen flow alternately,the entering air flowing inwardly through one or the other of thesepairs of courses and the nitrogen flowing outwardly through the one ofsuch pairs of courses not at any given moment serving for the inflow ofthe air. Through the third course, 26A, of the exchanger 21 and throughthe corresponding course, 22A, of the exchanger 22, but in the order22A, 2iA, the leaving oxygen product is discharged. Exchanger 22 has, asabove noted, a fourth course 22D, through which a portion of the airwhich is entering the apparatus by way of the exchangers 21, 22 iscaused to recirculate through exchanger 22, the better to effect thedepositing out of impurities from the entering air stream and to increasthe temperature of the air entering the expansion engine.

It has been noted, with respect to the exchangers 2i and 22, and, itwill be noted, with respect to further heat exchangers 23 and 24hereinafter to be described, that the courses are indicated as beingcoaxial. It will, however, be appreciated that the precise form ofconstruction of the exchangers is not illustrated in the diagram of Fig.1, since suitable multiple-pass exchangers may assume various forms,and, in the Samuel C. Collins application above identified, a suitableform of exchanger is illustrated, and other possible types areillustrated in Letters Patent Nos. 2,596,098 and 2,611,586, grantedrespectively on May 6, 1952 and September 23, 1952 upon otherapplications of said Samuel C. Collins, respectively Serial Nos. 3,217,filed January 20, 1948 and 2,877, filed January 1'7, 1948. Exchanger 23will be observed shortly to be of the four-course type, and exchanger211 of the threecourse type.

Conduit I5 communicates with course 2113 of exchanger 2 i, and conduitl6 with course 210 of exchanger 21. The leaving oxygen product passesoutwardly through course 21A of ex changer 2i and passes to a shop line,to a bank of cylinders, or to any other desired point or apparatus, forus or storage, through a conduit 25. Course 21C of exchanger 2| isconnected by a conduit M with course 22C of exchanger 22. Course 21B ofexchanger 21 is connected by a conduit 32 with course 2213 of exchanger22. A conduit 33 connects course 21A of exchanger 21 with course 22A ofexchanger 22. These courses are traversed serially, in the order 22A,21A, by the oxygen product, as later described. It will be appreciatedthat air will flow alternately in through course 21C, conduit 3! andcourse 22C or course 213, conduit 32 and cours 22B, while concurrentlynitrogen will flow outwardly through the ones of said courses andpassages last mentioned not carrying the entering air.

A suitable automatic reversing valve mechanism, generally designated 29,is provided beyond, in terms of entering air flow, the end of heatexchanger 22 last left by the entering air and first entered by theleaving nitrogen, this including four automatic check valves 41, 42, 43and 45. This arrangement is disclosed in the Samuel C. Collinsapplication Serial No. 661,253. The lower end of course 223 hasconnected with it a conduit 55 which leads to the check valve 41, and abranch 46 leads from conduit 45 to check valve 42. A conduit 41' leadsfrom course 22"to check valve ,and a branch 48% connects conduit 41, ata point between course 220 andthe check valve 44', with the check valve4-3. A conduit 49 connects the other side of check valve 43 with aconduit 59 leading from the check valve '44 toa suitable restrictordevice 5|, which creates a slight diiference between the pressure intheconduit 50 and the pressure beyond the device 5!, the latter pressurebeing on the order or two pounds less than the pressure in conduit 50-.A conduit 52 connects the conduit'to with the bottom of course 22D. Aconduit 53 leads from the side of check valve 44 opposite the conduit4?, to the outermost course of the heat exchanger 23. Nitrogen alwaysflows outwardly through conduit 53. A conduit 55 connects the side ofcheck valve 4 2 opposite the conduit 46- to the conduit '53. Each of thecheck valves 5!,42, 43, and 44 opens in the direction indicated by itsand prevents opposite flow.

The restrictor 5| is connected as at 56 to a chamber 5'! within the topof an evaporatorcondenser-Sfl having a suitably insulated casing 6t andhaving in said casing an oxygen conducting conduit or course 62' and anair conducting conduit or course 63' in close heat exchange relationwith each other. The conduit or course 63' isv connected at 64* with thechamber 5". The oxygen conduit or course 62 is connected by a conduit 65with the bottom of course 22A of exchanger '22. The top of course 22D ofexchanger 22' is connected by a conduit tit with a conduit 51leadingfrom the chamber 57, and the reunited stream of air passes to aconduit 10, which leads to the. expansion engine I8 later more fullydescribed.

The connections of the downstream side of the restrictor 51 with thechamber 63 and with the conduit 61 have been shown as having the chamber51 common to them, but the use of a chamber in the casing of theevaporator-condenser iii! to effect such connections is not essential.

When the air entering the system is passing through course 223, it flowspast the check valve 4t. When course 223 is serving for outflow ofnitrogen, the nitrogen flows from conduit 53-, through conduit 55 andpast check valve 42 and through: conduitstt and 45 to course 22B. Whencourse 220 is serving for inflow of air, the entering air flows past thecheck valve 43. When course 220 is being used to conduct leavingnitrogen, the nitrogen fi'ows past check valve 44 and through conduit41. As the entering air is at a much higher pressure than the leavingnitrogen, no check valve subjected on its discharge side to air can beopened by the lower nitrogen pressure.

For best performance, as well during high pressure as during lowpressure production, the arrangement of exchangers 2| and 22 hereinshown and described is preferable. It is desirable that the entering airpass upward through exchanger 2| in order that the water frozen out ofthe entering air stream, and all of which is removed in exchanger 2!,may drain by gravity downwardly in that exchanger. Exchanger 22,however, is desirably so arranged that the at least nearly completelyliquid leaving oxygenstream which enters it during high pressure oxygenproduction shall pass upwardly therethrough. The flow of the enteringair is in oppositedirections through exchangers Zland 22 in a preferredarrangement. For low pressure oxygenproduction and/or with constructionsof ex- 6. changer 22 in which oxygen flow is suitably ratarded, anarrangement may be used which the oxygen may pass downwardly exchanger2-2'a-s well as in exchanger 2| while the air passes upwardly in both ofthe same.

The heat exchangers 23 and 24 have been previously mentioned. Exchanger23 has four courses: a central one-, ZEA, a next course 23B, a third"course 230, and an outer course 2313- surrounding,- as shown on thedrawings, course 23C. Obviously the arrangements of the courses,- andthestructure of this exchanger, are subject to wide structuralvariations. Exchanger 24 has a central course 24A, an outer course 240and an intermediate course 2 4B. It too is subject towide structuralvariation. It will be understood that the several courses will'be ingood heat exchange relation with respect-to each other.

It has been noted-that the-conduit misconnected with the outermostcourse 23D or exchanger 23. This connection is withthe top of suchcourse. The bottom of course 23]) is con-'- nectediby a conduit tfl'with the bottom ofcourse 24C of exchanger 24,. and the top of course 24Cis connected by a conduit H with the nitrogen outlet the eii-iuxconnection) 1-2 of a single col- The compressed air course 83ofev'aporat-or condenser $01 is connected by a conduit 14 with the topof 'course iz-3B of exchanger 23'. The bottom of said course isconnected by a conduit 15- with: a valve device t6, which, in theparticular apparatus shown, and when the latter is used for oxygenproduction, is adjusted to effect a pressure drop between its oppositesides on'the order of 88' p. s. i. for a compressor delivery pressureof'l60 p. s; i. is substantially thesanie reduction. in pressure asoccurs'in the expansion engine later described, when the latter is.operating. with. its longer period of admission,- hereinafter 'iul'lyexplained. The downstreamside of valve device 16 is connected with aconduit H which. leads to a condenser coil or element 18 in the lowerend of. the column T3. The central course (as shown) 23A of exchanger23. is con nected at itstop with a conduit: F9 leading to the oxygencourse 62' of the evaporator-condenser 69,. while its bottom isconnected with the bottom Of central course 24A of exchanger '25 by aconduit so. A conduit 81 leads from the top of the centralv course NA.This is connectedwith the discharge; of a liquid oxygen pump, laterdescribed. The condenser unit 18* is connected at its other end (fromthe conduit 17 by a conduit 82,. with the intermediate course 24B ofexchanger 24. The top: of course 24B is connected with. a conduit 83.,of which more will be shortly said.

Three of the four courses of exchanger '23 have been noted. The fourthcourse, 2'30, is connected at its top with an expanded air conduit 85,and itslower end is connected by a conduit; containing a check valve 81.openable towards the conduit. 1 and connected with the latter by aconnection 88; The check valve opens towards the conduit Tl, but onlywhen the pressure in the conduit 86 issuiiicient to effect opening ofcheck valve 8'1 against the: pressure in conduit 11.

The expansion engine l8, which may be of the construction shown in theSamuel C". Collins application, Serial No. 665,206, filed April 26,1946, and now -matured into- Patent No. 2,607,322, granted August 19,1952, provided with suitable means for predeterm-inedl'y lengthening andshortening the period of admission, or which may beof the character ofthe expansionengine employing cam follower rollers one or both of whichcoact with a cam depending on whether early or late cutoff is desired,which expansion engine is illustrated and described in an application ofWin W. Paget, Serial No. 31,017, filed June 4, 19%8, and now Patent No.2,678,028, granted May 11, 1954, or of other suitable construction,includes a cylinder 90 having admission and exhaust valves, not shown,and to the admission valve of which air under pressure is admitted fromthe conduit I9 through a conduit 9I with which an In surge tank 92 isconnected so as to minimize fluctuations in flow. A discharge or exhaustconnection 93 leads from the expansion engine to a Discharge surge tank94, which may have associated with it a strainer to catch any snow thatmight otherwise attain to the column while the heat exchangers 2| and 22were not fully cooled down during the starting of the apparatus. Theexpansion engine supports on the top of its cylinder a jacketed liquidoxygen pump 95 of any suitable construction, the liquid oxygen pumpbeing for example actuated by the expansion engine piston as is the pumpshown in the last above mentioned patent of Win W. Paget, or in anyother suitable manner; and it may be noted that the conduit BI isconnected with the discharge of the liquid oxygen pump 95, while thispump has asuction connection 96 leading to it from a strainer 91 whichis cooled or jacketed by liquid air, the jacket herein being representedby a coil 98. To the strainer 91' a conduit I09 leads from theevaporator-condenser at the bottom of the column 13, the conduit I99communicating with the condenser-unit-enclosing chamber IOI in thebottom of the column at a point at the desired liquid oxygen level inthe latter.

The Discharge surge chamber 94 has connected with it a conduit I05 whichis connected to a valve structure I96, which valve structure includes apassage or chamber IIlI continuously in communication with the conduit85, and another chamber connected through a conduit I09 directly withthe interior of the column at a point spaced an appropriate distancefrom the top of the latter. The valve structure I05, which may be calleda bypass valve, is adapted to have the two chambers mentioned connectedin communication with each other, and thus to connect the Dischargesurge chamber 94 in free communication with the upper part of the columnthrough the conduit I05, valve structure I06, and conduit I99. In thedrawing the constant communication between the conduits I95 and 85 isindicated by the passage I91, and the communicability of the passage orchamber I91 with the conduit I09 is indicated by the valve I08. Otherconstructions suited to the functions mentioned may evidently be used.

The expansion engine I8 is provided, in the present particularapparatus, with valve gear adapted to permit the engine to operate withadmission for a relatively short portion of its working stroke, or withadmission for a considerably longer portion of its working stroke. Aswill later be explained more in detail, when cutoff is relatively latein the working stroke to provide said long admission, the valvestructure I05 will prevent communication between the Discharge surgechamber 94 and the column through the conduit I99; and whencommunication between the Discharge surge chamber 94 and the column iseffected by the appropriate adjustment of the valve structure I06, theexpansion engine will be operated with admission for said relativelyshort portion of its working stroke.

Various means can be provided for efiecting the desired changes inperiod of admission, as, for example, with a cam opened admission valveas shown in the Samuel C. Collins Patent No. 2,607,322, granted August19, 1952, the provision of selectively operable cams with diiierentdwells, or cams one relatively adjustable with respect to the other. Seealso for example Ferguson, 2,221,790, patented November 19, 1940. Orcamfollower rollers one or both cooperating with a cam depending onwhether early or later cutoff is desired may be employed, as in theapparatus of the Paget Expansion Engine application.

Only such air will flow through the evaporatorcondenser 69 as cannotpass through the expansion engine. During 50-pound oxygen production,complete condensation of the fraction of air passing through the aircourse 63 of the evaporator-condenser 69 may conceivably be efiected,but if more air passes through this course than can be condenser by theavailable cold provided by evaporation of liquid oxygen, at a pressureon the order of 50 p. s. i., in the course 92 of theevaporator-condenser 60, the excess unliquefied air will be condensed inevaporator-condenser T8.

The conduit 83, previously mentioned, leads to a valve device i it!which is adapted to be adjusted to effect a reduction on the order of 60p. s. i. in the pressure of the fluid (liquid air) which flows throughit; and the downstream side of the valve device Iii is connected by aconduit III with the jacket 98 for the strainer 97 and the top of thisjacket is connected by a conduit I I2 with a jacket N3 of the liquidoxygen pump 95, there being a conduit H4 leading from the jacket H3 to aconnection H5 through which liquid air may be admitted to the top of thecolumn 13.

The column I3 may be of any suitable construction, and is illustrated asof the conventional packed type. It may obviously assume various forms,and the now abandoned Samuel C. Collins application, Serial No. 26,395,filed May 11, 1948, and the Samuel C. Collins Patent No. 2,610,046,granted September 9, 1952, show columns which are well adapted for thepurpose for which the present column is employed.

Before describing in detail the mode of operation of the apparatus shownin Fig. 1, it is desired to point out that the column may normally beoperated with a pressure on the order of 6 or 7 p. s. i., and in orderto evaporate liquid oxygen with the latent heat of condensation of airunder pressure in the condenser "IS, the pressure of the air in saidcondenser should be on the order of '70 p. s. i., and accordingly thevalve H0 will be set to maintain a differential in pressure of about 60p. s. i. between its upstream and downstream sides, the downstream sidebeing substantially at column pressure, and the upstream sidesubstantially at a pressure of 70 p. s. i. The expansion engine, whenworking with the later cutoff, has an expansion through it at leastsubstantially equal to the difierence between 158 p. s. i., the pressurein line "I9, and the pressure in the line TI. Thus the expansion engineprovides a pressure drop on the order of 88 p. s. i. This 88 p. s. i.drop, plus the 70 p. s. i. pressure previously mentioned, plus thedifferential in pressure of about 2 p. s. i. provided by the restrictor5i, gives a cumulative pressure of 160 p. s. i.; and that is thepressure at which the two-stage compressor, not shown, which deliversair to the conduit ll, may deliver air, continuously. It is to ibe-notedthat the conduit I and valve device 75 are substantially in parallelwith the expansion engine and the check valve 87, and accordingly thevalve device i6 is set to give a pressure reduction on the order or '88p. s. i., so that the air starting at 158 p. si in the chamber 51 andpassing through the air course 63, conduit 14, heat exchanger course233, conduit 1:5 and past valve device it may attain to the pipe H atsubstantially the pressure at which the air is delivered through theconduit 88. Thus, it may be observed that the sum of the columnpressure, plus the reduction inpressure at the valve device 5 l 0, plusthe pressure reduction across the valve device it, plus the 2 p. s. 1.drop through the restrictor 5| and plus the resistance in variousconduits also equals .160 p. s. i., the delivery pressure of thecompressor supplying compressed air to the cenduit I l.

Another valuable function of passing a portion of the entering airthrough the evaporator-condenser resides in the fact that under varyingconditions, the expansion engine, though it may normally take a, certainpercentage of the air to be processed, may at times take somewhat largerquantities; by having a substantial stream of air normally passingthrough the evaporatorcondenser, there is available, in the event theexpansion engine requires more air by virtue of fortuitous changes inoperating conditions, air in the system which can be diverted andsupplied to the expansion engine and so enable to supply pressure to thelatter to .be maintained constant.

The mode of operation of the described apparatus during the productionoioxygen is different, depending upon whether 50-pound oxygen or oxygensuitable for cylinder charging (say at 2.000 .p. s. i is being produced.Oxygen at either pressure may be delivered. The mode of operation forthe production of oxygen at 50 p. s. 1. pressure will be describedfirst, and then the differences when oxygen at .2000 p. s. i. is to bethe product will be explained. Following this, a

procedure to set the plant in operation will be described.

Air is supplied continuously, as above noted, through the conduit II at300 K. and 160 p. s. i., from any suitable compressor. Ordinarilyatwostage compressor with an aftercoole-r may be used as the source ofair supply.

The entering air contains water vapor and carbon dioxide. These arecaused to be separated out of the air stream by cold supplied by theleaving streams of oxygen product and nitrogen. The carbon dioxide islargely deposited. in the heat exchanger 22 upon the walls of thecourses 22B and 22C, and the water vapor, as liquid water and as ice, inthe courses 22B and 24C of exchanger 21 and it may be of interest at thepresent moment to point out that the liquid oxygen drawn from thechamber H2! in the column 13 through conduit I09, the strainer $7, andconduit 55, is pumped by the liquid oxygen pump $25 through the conduit8! through the course 24A of heat exchanger 24, through the conduit 8%,,the course 23A of heat exchanger 23, conduit 19, the oxygen course 6201.the evaporator-condenser fiil, the conduit 55, course 22A of heatexchanger 22, conduit 33, and the course 21A of the heat exchanger 2i,and finally is delivered at the desired terminal pressure through theproduct delivery pipe 25. As has been previously pointed out, thenitrogen leaving the column by way of the connection 12 passes throughthe conduit ll, through course 240 of heat exchanger 24, through conduit68, through course 23D of heat exchanger 23, through conduit 53, throughone or the other of the courses 2213 or 22C of heat exchanger 22,through one or the other of the conduits 35 or 32, through one or theother of the courses 213 or MS of heat exchanger 2l, through one or theother of the conduits IE or 16, and through the escape it, having passedthrough appropriate passage means in the va.ve mechanism I2. Thus itwill be evident that the streams of oxygen and nitrogen passing throughthe heat exchangers 22 and 2| will cause the carbon dioxide and watervapor to be condensed, or condensed and frozen, on the walls of thepassages in these exchangers through which the entering air may at anygiven moment be flowing, and that liquid water will be evaporated orentrained, and deposits of ice and carbon dioxide snow sublimed, and becarried out, by the leaving nitrogen stream, of the passages in whichthey have been deposited. A portion of the air which is passed throughthe heat exchangers 2l and 22 is caused to pass again through the heatexchanger 22, through the course 22]) thereof, as previously explained,flowing through the conduit 52, course 22D, and conduit 5'6 andrejoining the main mass of air .Which passes, during the production oflow pressure oxygen, through the chamber 51 and conduit 61; and thereunited streams pass through the conduit it and the conduit e1 into theexpansion engine to be expanded therein and to be cooled by theperformance of work during the adiabatic expansion of the fluid in theexpansion engine. The flow through conduit 52, course 22D of heatexchanger 22, and conduit is caused by the device 5|, which providesapproximately a 2- pound difference in pressure at its opposite sides.

At this point it may be noted that, regardless of the pressure of thedelivered product, some of the air supplied to the apparatus fortreatment therein always passes through the expansion engine [8, andsome of the air always passes through evaporator-condenser so, thequantity of air passing through evaporator-condenser 60 being determinedby the cutoff of the expansion engine. When the expansion engineoperates with relatively early cutofi, more air necessarily passesthrough evaporator-condenser Gil. During the production of oxygen at 50p. s. 1., about 12% of the total mass of entering air passes through theair course '63 of evaporator-condenser 8B in heat exchange relation withthe leaving oxygen product. When oxygen at 2000 p. s. i. is the desiredproduct, as much as 60% of all the air may pass through the air course63 of evaporator-condenser til. The air which leaves the heat exchanger22 on its way to pass through the chamber 5? of evaporator-condenser 60and flow through the conduit 6? is at a temperature of K. and a pressureof p. s. i. At the downstream side of the restrictor device 5! thepressure is 158 p. s. i. The recirculated air which flows through theconduit 65 is at a pressure of on the order of 158 p. s. i. and atemperature of K. just before it joins the fluid stream in conduit 6'5.When the streams have been mingled in the conduit it, all the air is ata temperature of 135 K. and a pressure of 158 p. s. i. The portion ofthe air which flows through the conduit Hi and does work in theexpansion engine leaves the latter at a temperature of 110 K. and. apressure of 70 p. s. i. when 50- pound oxygen is to be produced. Thisexpanded air passes through the conduit 8'5, through course 230 of heatexchanger 23, and emerges at a temperature of 105 K. and a pressure of70 p. s. i., and passes the check valve El to mix with liquid air whichhas passed the valve device It, and there is formed a stream partiallyof liquid air and partially of expanded air at a temperature of 100 K.and a pressure of '70 p. s. i. It may be observed that the air from theair course 63 of the evaporator-condenser 6i} emerges from heatexchanger 23 and enters the conduit T5 at a temperature of 112 K. and apressure or 158 p. s. i. After passing through the valve device 76 andundergoing a drop in pressure of about 88 p. s. i.,

the liquid air is at the same pressure as the expanded air comingthrough conduit 86.

The mixture of liquid air and expanded air at a temperature of 100 K.and a pressure of 70 p. s. i. enters the condenser coil i3 and iscondensed by reason of the giving up of heat in the process ofvaporizing oxygen in the bottom of the column. The liquid air emergingfrom the condenser 78 is at a temperature of 96 K. and a pressure of '70p. s. i., and after this liquid air has passed the valve device H andhad its pressure reduced by approximately 60 p. s. i., the liquid airwill be at a temperature of 83 K. and a pressure of about 9 p. s. i.Following the jacketing of the oxygen strainer 91 and the liquid oxygenpump 95, the still liquid air will enter the top of the column at atemperature of 83 K. and a pressure of about '7 p. s. i., and it will berectified therein so that substantially pure oxygen (99.5%

pure, at least) can be drawn from an appropriate point in theevaporator-condenser arranged in the bottom of the column at atemperature of 95 K. and a pressure of 7 p. s. i., or perhaps less. Thisliquid oxygen will flow through the strainer 91, conduit 96, the liquidoxygen pump 95, the conduit 8|, and the central courses, in series. ofheat exchanger 25, heat exchanger 23, evaporator-condenser Ell, heatexchanger 22, and heat exchanger 2!, and emerge, when 50-pound oxygen isbeing produced, in the form of gaseous oxygen at the mouth of theproduct pipe 25.

When oxygen for cylinder charging is to be produced, the valve structureHi6 will be operated to connect the conduits I85 and IE9 and theexpanded air leaving the expansion engine will then pass through theconduit its, the valve structure I06, and the conduit I into the column,and the pressure of the air in the conduit it will be reducedsubstantially to that within the column, and accordingly no moreexpanded air will be discharged through the check valve 8'1, becausethis valve will be held closed by the pressure, on the order of 13 p. s.i., which subsists in the conduit 11. At the time the valve structure105 is operated to permit the exhaust from the expansion engine to passsubstantially directly into the column through the conduit I05, thepoint of cutoff of the expansion engine I8 will be changed to make itmuch earlier in the stroke; and, the speed of the expansion engineremaining unaltered, much lessroughly half as muchair can go through theexpansion engine. As a result of this, the air which cannot flow throughthe conduit 61 and be passed through the expansion engine will ofnecessity go through the air course 63 of evaporator-condenser 50, and,having passed through course 2313 of heat exchanger 23, this now muchlarger mass of air, perhaps 60% of the total mass, will pass through thevalve device l6 and enter the condenser coil N3 of theevaporator-condenser at the bottom of the column '83 and be liquefiedtherein. This larger volume could not be liquefied in theevaporator-condenser 66 and the heat exchanger 23 because the oxygen nowat a much higher pressure cannot be vaporized at the temperature ofcondensing air. The reduced volume of liquid air from condenser coil 18will pass through the heat exchanger 2% by way of course 243 and nextpass through conduit 83 and the valve device Hl] and then, afterjacketing the strainer ii! and the liquid oxygen pump 95, will be passedinto the top of the column for rectification. A much smaller percentageof the total oxygen content of the air entering the apparatus will bedelivered during the production of 2000-pound oxygen than during theproduction of 50-pound oxygen.

In starting up the apparatus, the valve 38 will be open and for aconsiderable period, on the order of two hours, and the expansion enginewill be operated with relatively late cutoff. This will mean that mostof the air will pass through the expansion engine, a desirable thing atthis time because there would be no oxygen to effect condensation of airin evaporator-condenser S8. The entering air through whichever coursesof heat exchangers 2| and 2. 3 it may pass, will, about 12% of it, flowthrough the evaporator-condenser 68, heat exchanger 23, valve device i6,condensing unit 18, exchanger 24, conduit 83, and past the valve deviceH0 through the jacket for the oxygen strainer 91, the jacket H3 for theliquid oxygen pump 95, and then through the conduit Il and connection H5into the top of the column '13. During a considerable portion of thestarting operationthe cooling down period-this air will simply flow outthrough the conduit H, etc. and be discharged. The relatively largeamount, about 88%, of the air which passes through the expansion enginel8 will pass into the column through the conduit I 99, and it too willdischarge through the conduit H to the atmosphere. As the unit coolsdown, a little liquid will com mence to form, and as soon as this stageis reached, the expansion engine will be shifted to early cutofi, thusincreasing the refrigeration, and for another period, perhaps an hour,the exhaust from the expansion engine will still continue to bedischarged through the connection m9 into the column. When the liquidfinally builds up high enough so that oxygen can be drawn through theconduit M9, the apparatus will be ready to go to ZOOO-pound oxygenproduction, or, by closing the valve I08 and making the point of cutofiin the expansion engine much later, 50-pound oxygen canbe produced. Itwill be noted that during the later stages of the cooling downoperations, the bypass valve 5% will still be open and the expansionengine Will be working with an early cutoff, and that when the liquidlevel in the column reaches the overflow point, the machine will beready to fill cylinders, but if 50-pound oxygen be desired, the bypassvalve can be closed and the valve gear arranged in the expansion enginefor late cutofi.

Certain points not previously mentioned, or perhaps deservingreemphasizing, may be noted now with respect to the apparatus which hasso far been described. The motion of the recirculating air flowingthrough the conduit 52 is counter-flow relative to the entering airstream, and, as previously observed, it is caused to take place byproviding a slightly less resistance to accuse 13 flow through. thecourse 22D of heat. exchanger 22 than to fiowvpast. the device andthrough the chamber 51 of evaporator-condenser 60..

Asaportion'a minimum of about l2%-of the entering air always passesduring normal operation through the evaporator-condenser 6'0 inheat-exchange relation with the fluid flowing through the oxygen productline, there will al ways, as soon as low enough temperatures areattained, be some liquid. passing into the top of the'column.

During the cooling down period, and also when oxygen: at 2000 p. s. i.the desired product, the expanded air may enter the column through thevalve controlled connection. [09' at a point perhaps three-quarters ofthe way up the. column, instead of having to pass around through heatexchanger, the conduit 86 and the check valveu8'l. Indeed, no air canthen pass through the circuit last mentioned, because theair in theconduit ll will be at a pressure so much greater than the pressure inconduit 85, as to maintain the check valve closed.

During the production of 50-pound oxygen, the main flow of expanded air(about 88% of. the total entering air) passes into the top of course230. of heat exchanger 23 and passes down: through this heat exchangerin heat exchange relation both. with liquid oxygen produced. in thesystem and with the leaving nitrogenstream. The expanded air, at 105 K.and 70 pts. i. pressure-the same pressure as at release from theexpansion enginethen passes through the one-way check valve 8? andenters the condenser unit 18 in the bottom of the column, andv theexpanded air is condensed, its latent heat'of condensation serving toevaporate liquid oxygen at a lower pressure in the bottom of the column.The liquefied air goes into the bottom of heat exchanger 24 and gives upsome of its heat to the nitrogen and to the liquid oxygen which alsoflow through: exchanger 24, and then passes through the valve device H0,which causes a reduction in pressureonthe order of 60 p..s. i., thisresulting in a further cooling of the liquid air and some vaporization.After passing around the liquid oxygen filter which it jackets, theliquid air is used, as will be recalled, to jacket the liquid oxygenpump also, and it then enters the top of the column at a temperature of33 K. and at a pressure of on the order of 7 p. s. i. The process ofrectification in the column results in there being available liquidoxygen in the evaporator-condenser at the bottom of the column,specifically in the chamber Ill-t surrounding the condenser unit 18, ata temperature of about 95 K. and a pressure of around '7 p. s. i., whilenitrogen, with the single column rectifier, containing from 7 to oxygen,and; at a temperature of 83 K. and a. pressure of 7 p. s. i., passes outof the" top of the column. The liquid oxygen is filtered as it passes tothe liquid' oxygen pumpand is forced by the latter at a pressurecommensurate with the desired product pressure successively through heatexchanger 24, heat exchanger 23, evaporator-condenser 60; heat exchanger22, and heat exchanger 21 tothe point of product delivery, absorbingfrom the entering air stream the heat necessary to vaporize it, when50-pound oxygen is being produced, while passing throughevaporator-condenser 60, and the absorbed heat resultingin a change ofstate of the enteringair from gaseous to liquid form- When 2000-poundoxygen is being produced, the liquid oxygen cannot be evaporated theevaporator-condenser 60 and. so there is simply a temperature increaseof a few degrees in the oxygen passing throughv evaporator-condenser69., the evaporator-condenser 60 then operating simply as a heatexchanger; Nevertheless, when oxygen. at 2000 p. s. i. pressurereachesthe cylinders to which productrline 25. may be connected, this oxygen isin a vapor state. The valve devices 15 and H 0 will be adjustecl: asnecessary to efl'ect the desired operating characteristics at all timesand. at whatever product pressure.

During: the production ofv 50-pound oxygen, the portion of the air thatsplits off from the main stream in the header of evaporator-condenser6B'-an. amount which may be 12% of the whole during normal 50-poundoxygen production-is largely condensed in evaporator-- condenser '55:and. any excess that may pass through the evaporator-condenser 60without liquefaction. will be liquefied in the evaporator coil 18. If2000-pound oxygen is the product, noexpanded air enters theevaporator-condenser "38 with the air going by way of exchanger 23 fromthe evaporator-condenser 60, as the low pressure of the expandedair-this air hasbeen expanded through a. much, greater range ofexpansion. when the expansion engine is working with early cutoifwillnot permit it to effect opening of the check valve 81 even though theexhaust from the expansion engine communicates freely withthe checkvalve 81. Note that the exhaust from the expansion engine communicatesfreely through the conduit I 09' with the column at this time. Thelarger quantity of air going through. the evaporator-condenser 69" andheat exchanger 23 and entering the condenser ?8, even though little ofit may have been condensed before the arrival at the condenser 18, is ata pressure of 70 p. s. i. suited for condensation by the latent heat ofevaporation of oxygen which is vaporized in the chamber NH. The total.quantity of oxygen produced when 2000-pound oxygen is being suppliedwill be proportionately much: less than when SO-pound oxygen is the end.product. It may be noted that the exhaust pressure of the expansionengine during the production of 2000-pound oxygen will be essentiallythe same as column pressure, namely 7 p. s. i.

Roughly, during cylinder charging (2000- pound production) 40% of theair goes through the expansion engine and directly into the column.while the other 60% follows the coursenormally taken during. 50-poundoxygen. production by but 12% of the air supply to the apparatus. Thischange in the air flow distribution is due to the much earlier cutoffwhich occurs during 2000-pound oxygen production. It will be understoodthat the expansion engine operates at a predetermined speed, that thequantity of fluid which can pass through it is accordingly determined bythe point of cutoiT, and that, accordingly, with late cutofi, a muchlarger percentage of the total entering air stream can pass through theexpansion engine than when cutoff is made early.

With an apparatus having, during low pressure oxygen production, thetemperatures and pressures above mentioned, the relatively later cutoffof the expansion engine would theoretically take place at about 70% ofthe working stroke; and during high pressure oxygen production therelatively early cutoff would be at theoreticall'y on the order of 2 5%of the working stroke,

but these percentages are only illustrative. For example, there are twofactors which in practice would tend to call for later cutofi in bothmodes of operation, namely, that it is desirable in practice to handleat least a little larger than the theoretical mass of air to insureadequate refrigeration, and, moreover, with actual apparatus, theexpected temperatures and pressures are not always attained.

By sending the expanded air through the top three or four trays of thecolumn, the liquid air flowing downward can be caused to wash a fractionof the oxygen from the expanded air.

During the production of -pound oxygen, the percentage of oxygen in thewaste gas leaving the top of the column is approximately 10% andtheoretically might be as low as 7%. The per centage of oxygen in theliquid air which is fed into the top of the column is approximately 21%.

The percentage of oxygen in the liquid which is in equilibrium withgaseous air of 21% oxygen is approximately 47%. As long as descendingliquid has less than 47% oxygen in it, it can extract some oxygen fromair passing directly into the column.

Refrigeration is obtained from the Joule- Thomson eliect, and from theoperation of the expansion engine. The Joule-Thomson efiect givesapproximately 2 K. of cooling. During normal Ell-pound production, 12 K.of cooling is obtained from the expansion engine. When filling cylinders(producing oxygen at 2000 p. s. i.), the expansion engine provides 42 K.cooling of the air which passes through it, but only 40% of the totalair stream passes through the expansion engine. The 2 K. of coolingobtained by the J mile-Thomson effect as well as the 12 K. coolingobtained from the expansion engine applies to the flowing stream ofentering air.

The nitrogen, as above noted, was at 83 K,

and a pressure of '7 p. s. i. in conduit 1 i. In conduit 53 it is at 109K. and 5 p. s. i. Between the exchangers 22 and 2! it is at 176 K. and 3p. s. i. The leaving oxygen product is at 178 K. between the heatexchangers 22 and 2!, and in the conduit B5 is at 110 K. The enteringair between heat exchangers 2| and Z2 is at 184 K. and 160 p. s. i. Allpressures and temperatures are, of course, approximate.

The apparatus shown in Fig. 1 and above described is illustrated,described and claimed in by copending but now abandoned applicationSerial No. 122,077, filed October 18, 1949, as is also the methodhereinabove disclosed, and these will also be found disclosed andclaimed in my application Seriai No. 383,541 filed of even dateherewith. The invention of this present application involves the use ofa double column, and will be the more readily comprehended in view ofthe explanation of the single column method and apparatus. It involvesboth method and apparatus claimed from the double column aspect hereinand also claimed generically in the other applications mentioned in thisparagraph.

Fig. 2 discloses an oxygen generator in accordance with the inventionand incorporating a double column 1241. Much of the structure of Fig. 2corresponds to that of Fig. 1, and the principal differences reside inthe utilization of the double column and the changes which that makesnecessary.

. The column i211 includes a high pressure chamher or section l2! and alow pressure chamber or section 1222, providing high and low pressurestages, and these are separated by a partition wall 123 which isprovided with a plurality of depending heat exchange elements 12% openat their ends communicating with the chamber l22 and closed at theirbottom ends I25. An inclined annular wall I28 projects inwardly at thetop of the high pressure chamber I21 and underlies a substantial numberof the depending heat exchange elements 124. The conduit 11 in Fig. 2bears the same relation to the check valve 3! and to the valve device 76which it bears in Fig. 1, but it communicates at [23 with the highpressure chamber l2! of the double column, near the bottom of thatchamber. Accordingly, liquid air and expanded air pass into the bottomof the high pressure chamber i2i in a united stream. When the apparatusis operating to produce oxygen, substantially pure nitrogen (about 98%pure) drips from the heat exchanger elements 124, and a portion of it iscollected in an annular trough 529 which is formed between the annularsloping wall 128 and the outer wall of the column. From this trough 129a conduit I30 conducts the liquid nitrogen to a heat exchanger 24' (afour-course one) and the nearly pure nitrogen passes through the course24C of this heat exchanger and then passes through a conduit l32 and avalve device H8, and from the latter through a conduit 533 to a coolingcoil or jacket 34 surrounding the strainer 97 for liquid oxygen. Thecooling coil 34 is connected in series with a jacket H3 for the liquidoxygen pump, and from this jacket a conduit I Hi leads to a connectingdevice 538 arranged in the top of the columns low pressure chamber 22.From the bottom of the high pressure chamber 21 of the double columnI29, a conduit Mil leads to the course 24'13 of heat exchanger 24, andfrom this course the enriched air which is formed in the chamber i2! bya process of partial rectification therein is delivered through aconduit it] to a valve device Ht" whose other side is connected by aconduit 842 with the connection M3 leading from a conduit M4 connectedwith the Discharge surge chamber 94 and also connected through thecasing of a bypass valve structure I with a conduit 145 which isconnected with the course 23'0 of the heat exchanger 23', The other endof the course ZSC is connected with the conduit 36 which leads to thecheck valve 81 and to the conduit 88 which communicates with the conduit1'? at a point in the latter just beyond the valve device 16. The liquidoxygen pump takes liquid oxygen from the chamber !22 via a conduit 58and the strainer 9'1 and discharges it through a conduit 8| into the topof course 242A of heat exchanger 24 and a conduit an, the course 232% ofheat exchanger 23, conduit '58, oxygen course 62 of evaporator-condenserBil. conduit 65, course 22A of heat exchanger 22, conduit 33, and courseZiA of heat exchanger 2!, delivering the oxygen pumped by the oxygenpump 95 to the delivery conduit The mode of operation of this apparatusdiffers from that first described in particulars which grow out of theemployment of a double column instead of a single column. The valvedevices i H! and HE" each control the flow of one of the fluids whichoriginated in the high pressure chamber 12! of the double column. Theyare therefore quite similar in construction and efiect like reductionsof pressure, herein approximately 75 p. s. i. One of them has the fluidpassing from its downstream side into the low pressure chamber 22 of thedouble column at a 17 point somewhat lower in that chamber than theother, as will be noted. The nearly pure nitrogen passes through theconduit I30, through course 24'0 of heat exchanger 24, through conduitI32, through valve device II conduit I33, cooling coil I34, jacket H3,conduit H4, and through the connection I36 into the top of the uppersection of the double column. The en riched air passes through theconduit I40, course 24'B of exchanger 24', conduit I4I, valve deviceIItI", conduit I42, and conduit I43 into the chamber I22.

Rectification takes place in the manner common to double columns in thetwo compartments of column I20. That nitrogen is nearly pure (98%) byreason of the rectification process which. goes on in chamber I2! hasbeen mentioned. Enriched air that leaves the bottom of the chamber I2Icontains from 40 to 50% oxygen. The pressure in the lower section IZImay be between 75 and 85 p. s. i.; the pressure in the upper section I22from 5 to p. s. i. The pure oxygen drawn off from the bottom of chamberI22 may desirably be pumped at a pressure of approximately 50 p. s. i.through course 24A of exchanger 24', conduit 80, course 23'A ofexchanger 23', and conduit I9 into the oxygen course 62 ofevaporator-condenser 60. At this pressure the saturation temperature ofthe oxygen will be just a little below the saturation temperature of theinflowing air, at 158 p. s. i. Accordingly there will be, with thequantity of compressed air which flows during low pressure, 50-poundoxygen production, to wit, 12% of the whole, vaporization of the leavingoxygen and at least substantially complete liquefaction of the air whichpasses through the evaporatorcondenser 60. However, if completeliquefaction of this air does not occur, such liquefaction will takeplace in the high pressure chamber I2I of the double column.

It will be clear that the pressure drop in the expansion engine and thepressure drop caused by the valve device I I0", the pressure drop at therestrictor 5|, and the pressure in the chamber I22 of the columncumulatively amount to the pressure at which air is supplied to thesystem from the compressor. Likewise, in the parallel connection, therestrictor 5| with its 2 p. s. i. pressure drop, the valve device I6with 1 its 88 p. s. i. pressure drop, the valve device III? with its 60p. s. 1. pressure drop, and the pressure in the low pressure chamber I22cumulatively equal the supply pressure.

It will be clear from what has been said that with the present inventionthere is conservation of refrigeration in a highly desirable man- Asabove noted, compressed air at 160 p. s. i. may be condensed when thetemperature is reduced to say 112 K. when brought into heat transferrelation with liquid oxygen at a pressure of 50 p. s. i. and atemperature of 107 K. By pumping the liquid oxygen from the column andincreasing its pressure to the value given, and bringing it into heattransfer relation with the entering air in the evaporator-condenser 68,about 12% of the entering air can be liquefied, and during normal50-pound oxygen production, the periods of admission of the expansionengine may be so predetermined that just about 12% of the entering airwill not be capable of passing through the expansion engine and will becaused to flow through evaporator-condenser 60. If all this air is notliquefied in this evaporatorcondenser, this will do no harm because theair will in any event be condensed. If an oxygen product at an excess of50 p. s. i. were desired but in gaseous form, a much smaller oxygencompressor would be required with the use of my invention than if theinitial pressurization were not effected on th liquid oxygen.Appropriate valve device adjustments will be made as necessary whetherthe occasion therefor be fluctuating conditions or changes in productpressure.

It will be understood that by this invention arrangements are providedin which there is a substantial economy both of refrigeration and powerthrough the evaporation of liquid oxygen placed under a pressure abovecolumn pressure by a relatively small displacement pump, whichevaporation is effected by heat given up by a fraction of the enteringair when the same is condensed by th refrigeration provided by thevaporization of the liquid oxygen and this is also true of the improvedmethod. Other features and advantages have been pointed out above orwill be apparent from What has already been said, and require norepetition here.

It is to be understood throughout the foregoing specification thatpressures and temperatures are approximat in some cases, and that,moreover, pressure drops due to friction in pipes have generally goneunmentioned.

This application is a division of my application Serial No. 122,077,filed October 18, 1949, now abandoned and a continuation-in-part of mycopending applications, Serial No. 30,388, filed June 1, 1948, andSerial No. 81,589, filed March 15, 1949, both of which are alsoabandoned.

While there are in this application specifically described certain formswhich the invention may assume in practice, and certain illustrativeapplications of the improved method from its various aspects, it Will beunderstood that these have been disclosd for purposes of illustrationand that the invention from both of its major aspects may be modifiedand embodied in various other forms and practices without departing fromits spirit or the scope of the appended claims.

What is claimed is:

1. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, another heat exchanger, an expansionengine, a double column having high and low pressure chambers, a liquidoxygen pump, means for connecting said at least one heat exchanger todeliver air under pressure in divided streams to saidevaporatorcondenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the high pressure chamber ofsaid column via said other heat exchanger, means including a valvedevice for delivering air from said evaporator-condenser via said otherheat exchanger to the high pressure chamber of the column at the samepressure as the exhaust from the expansion engine, means for connectingsaid liquid oxygen pump with the low pressure chamber of said column ata point at the normal liquid oxygen level therein, and means forconducting the discharge from said liquid oxygen pump to saidevaporator-condenser.

2. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, another heat exchanger, an expansionengine, a double column having high and low pressure chambers, a liquidoxygen pump, means for connecting said at least one heat exchanger todeliver air under pres sure in divided streams to saidevaporator-condenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the high pressure chamber ofsaid column via said other heat exchanger, means including a valvedevice for delivering air from said evaporator-condenser via said otherheat exchanger to the high pressure chamber of the column at the samepressure as the exhaust from the expansion engine, means forrespectively effooting the delivery, at appropriately reduced pressures,of nearly pure nitrogen and of enriched air from the high pressurechamber to the low pressure chamber of said column, means for connectingsaid liquid oxygen pump with the low pressure chamber of said column ata point at the normal liquid oxygen level therein, and means forconducting the discharge from said liquid oxygen pump to saidevaporator-condenser.

3. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, another heat exchanger, an expansionengine, a double column having high and low pressure chambers, a liquidoxygen pump, means for connecting said at least one heat exchanger todeliver air under pressure in divided streams to saidevaporatorcondenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the high pressure chamber ofsaid column via said other heat exchanger, means including a valvedevice for delivering air from said evaporator-condenser via said otherheat exchanger to the high pressure chamber of the column at the samepressure as the exhaust from the expansion engine, means includingsimilar devices for maintaining like differences in pres sure betweentheir upstream and downstream sides for respectively efiecting thedelivery, at appropriately reduced pressures of nearly pure nitrogen andof enriched air from the high pressure chamber to the low pressurechamber of said column, means for connecting said liquid oxygen pumpwith the low pressure chamber of said column at a point at the normalliquid oxygen level therein, and means for conducting the discharge fromsaid liquid oxygen pump to said evaporator-condenser.

4. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heat exchanger, an evaporatorcondenser, another heat i exchanger, an expansionengine, a double column having high and low pressure chambers, a liquidoxygen pump, means for connecting said at least one heat exchanger todeliver air under pressure in divided streams to saidevaporator-condenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the high pressure chamber ofsaid column via said other heat exchanger, means including a valvedevice for delivering air from said evaporator-condenser via said otherheat exchanger to the high pressure chamber of the column at the samepressure as the exhaust from the expansion engine, means includingsimilar valve devices individual to each conducting means for conductingnearly pure nitrogen and enriched air at appropriately reduced pressurefrom the high pressure chamber to the low pressure chamber of thecolumn, means for connecting said liquid oxygen pump with the lowpressure chamber of 20 said column at a point at the normal liquidoxygen level therein, and means for conducting the discharge from saidliquid oxygen pump to said evaporator-condenser.

5. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, an expansion engine, a double columnhaving high and low pressure chambers, a liquid oxygen pump for imposingon the liquid oxygen product leaving the low pressure chamber anincreased pressure at which its latent heat of vaporization will besupplied by entering air in said evaporator-condenser, means forconnecting said at least one heat exchanger to deliver air underpressure in divided streams to said evaporator-condenser and to saidexpansion engine, means for delivering air exhausted from said expansionengine to the high pressure chamber of said column, means including avalve device for delivering air from said evaporator-condenser to thehigh pressure chamber of the column at the same pressure as the exhaustfrom the expansion engine, means including further valve devices forrespectively delivering enriched air and nearly pure nitrogen from thehigh pressure chamber to the low pressure chamber of the column, meansfor connecting said liquid oxygen pump with the low pressure chamber ofsaid column at a point at the normal liquid oxygen level therein, andmeans for conducting the discharge from said liquid oxygen pump, at theincreased pressure which said pump imposes on the oxygen, to saidevaporator-condenser for heat exchange in the latter only with enteringair.

6, In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, an expansion engine, a double columnhaving high and low pressure chambers, a liquid oxygen pump, means forconnecting said at least one heat exchanger to deliver air underpressure in divided streams to said evaporator-condenser and to saidexpansion engine, means for delivering air exhausted from said expansionengine to said high pressure chamber, means including a valve device fordelivering air from said evaporator-condenser to said high pressurechamber, means for effecting the delivery of fluids from said highpressure chamber to said low pressure chamber, means for conductingeffluent nitrogen from said low pressure chamber to said at least oneheat exchanger, means for connecting said liquid oxygen pump with saidlow pressure chamber at a point at the normal liquid oxygen leveltherein, and means for conducting the discharge from said liquid oxygenpump to said evaporator-condenser at a pressure at which vaporization ofthe liquid oxygen product may be effected therein at least largely byheat absorbed by the air passing through the evaporator-condenser andbeing liquefied therein.

7. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, an expansion engine, a double columnhaving high and low pressure chambers, a liquid oxygen pump, means forconnecting said at least one heat exchanger to deliver air underpressure in divided streams to said evaporator-condenser and to saidexpansion engine, means for delivering air exhausted from said expansionengine to said high pressure chamber, means for effecting the deliveryof air at a reduced pressure from said evaporator-condenser to said highpressure chamber, means including devices maintaining like pressuredifferentials between their upstream and downstream sides for efiectingthe delivery of fluids from said high pressure chamber to said lowpressure chamber, means for effecting the delivery of nitrogen to saidat least one heat exchanger via a course bypassing saidevaporatorcondenser, means for connecting said liquid oxygen pump withsaid low pressure chamber at a point at the normal liquid oxygen leveltherein, said liquid oxygen pump efiecting an elevation of the pressureof the liquid oxygen drawn from such low pressure chamber to a pointsuited for the vaporization of the liquid oxygen in saidevaporator-condenser by the liquefaction of air passing through thelatter, and means for conducting the discharge irom said liquid oxygenpump to said evaporator-condenser for vaporization therein.

8. In an apparatus for the separation of gases by the liquefactionandrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, an expansion engine, a double columnhaving high and low pressure chambers, a liquid oxygen pump, means forconnecting said at least one heat exchanger to deliver air underpressure in divided streams to said evaporator-condenser and to saidexpansion engine, means for delivering air exhausted from said expansionengine to said high pressure chamber, means including a valve device fordelivering air at a reduced pressure from said evaporator-condenser tosaid high pressure chamber, means including valve devices providing likepressure differentials between their upstream and downstream sides foreffecting the delivery of fluids from said high pressure chamber to saidlow pressure chamber, means for effecting the delivery of nitrogen tosaid at least one heat exchanger via a course bypassing saidevaporator-condenser, means for connecting said liquid oxygen pump withsaid low pressure chamber at a point at the normal liquid oxygen leveltherein, said pump efiecting an elevation of the pressure of the liquidoxygen drawn from such low pressure chamber to a point suited for thevaporization of the liquid oxygen in said evaporatorcondenser by theliquefaction of air passing through the latter, and means for conductingthe discharge from said liquid oxygen pump to said evaporator-condenserfor vaporization therein.

9. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingcompressed air through at least one heat exchanger, dividing the air,passing a portion thereof through an expansion engine, passing anotherportion through an evaporatorcondenser, combining said portions, passingsaid combined portions into the high pressure stage of a double column,taking oxygen-rich liquid from said high-pressure stage, reducing thepressure thereof, and delivering it into the low pressure stage of saiddouble column, taking nitrogen from said high pressure stage, reducingthe pressure thereof, and delivering it into the low pressure stage ofsaid double column, withdrawing nitrogen eiiiuent from the low pressurestage of said column and delivering it past said evaporator-condenser tosaid at least one heat exchanger, withdrawing liquid oxygen from the low22 1 pressure stage of said column and pumping it, at a pressure higherthan the pressure within said low pressure stage, through theevaporatorcondenser in heat exchange relation with the air passingthrough the latter, and utilizing in the evaporator-condenser at least aportion of the heat of liquefaction of the air to vaporize at least themajor part of the oxygen at a pressure substantially above rectifierpressure.

10. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingcompressed air through at least one heat exchanger, dividing the air,passing a portion thereof through an expansion engine, passing anotherportion thereof through an evaporator-condenser, combining saidportions, passing said combined portions into the high pressure stage ofa double column, taking oxygen-rich liquid from said hi h pressurestage, reducing the pressure thereof, and delivering it into the lowpressure stage of said double column, taking nitrogen from said highpressure stage, reducing the pressure thereof, and delivering it intothe low pressure stage of said double column, Withdrawing liquid oxygenfrom the low pressure stage of said column and pumping it, at a pressurehigher than the pressure within said low pressure stage, through theevaporator-condenser in heat exchange relation with the air passingthrough the latter, and utilizing in the evaporator-condenser at least'aportion of the heat of condensation of the air to vaporize the oxygen ata pressure substantially above rectifier pressure.

ll. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingcompressed air through at least one heat exchanger, dividing the air,passing a portion thereof through an expansion engine, passing anotherportion thereof through an evaporator-condenser, reducing the pressureof said another portion to a value corresponding to that of expansionengine exhaust, combining said portions, passing said combined portionsinto the high pressure stage of a. double column, taking oxygen-richliquid from said high pressure stage, reducing the pressure thereof, anddelivering it into the low pressure stage of said double column, takingnitrogen from said high pressure stage, reducing the pressure thereof,and delivering it into the low pressure stage of said double column,withdrawing liquid oxygen from the low pressure stage of said column andpumping it, at a pressure higher than the pressure within said lowpressure stage, through the evaporatorcondenser in heat exchangerelation with the air passing through the latter, and utilizing in theevaporator-condenser at least a portion of the heat of condensation ofthe air to vaporize the oxygen at a pressure substantially aboverectifier pressure.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,078,953 Levin May 4, 1938 64,891 Rice Mar. 22, 19492,552,451 Patterson May 8, 1951

